This invention relates to an IC card, which is used as a cash card or a credit card issued by a financial institution such as a bank, and also which includes an integrated circuit permitting reliable data writing in it.
The present time has been called a cashless era, and goods can be purchased without using cash simply by utilizing cards issued by credit card companies or the like. Plastic cards, embossed cards, magnetic stripes cards, etc. are usually used as cash or credit cards. These cards, however, have structures which can be easily forged, and their improper use is a significant problem. To solve this problem, an information card has recently been developed which is commonly termed an IC card, in which an IC circuit with a secret key number, etc. stored therein is assembled such that the secret key number can not be readily externally read out. This IC card is difficult to forge and thus has excellent security, and it can also store a large quantity of information.
In the above IC card, usually various data are written with a combination of a CPU (Central Processing Unit) and an EPROM (erasable programmable read-only memory). Data supplied from an external terminal (i.e., a card terminal) is directed through the CPU to a particular address in the EPROM.
However, when there is abnormality in a memory area of the EPROM corresponding to a particular address when writing desired data in the IC card, the writing of data is disabled even though the rest of the EPROM is sound. In this case, the IC card itself is rendered to be invalid.